"Potentially Most Accurate Load"??

[zardoz]

Guess I've been working up this question for awhile now.

OK, in the short time I've delved into hand loading (since November 2008), I've amassed a few tools, books, lead supply, brass, etc.

I quickly went from "most velocity and power" loader, to a "highest accuracy" loader.
Doesn't matter how much power it has, unless you can consistently achieve target I've found.

So, in loading for the .223 Remington, I found that the Lyman "Potentially Most Accurate Load" recommendations have some merit in my own shooting. A cartridge I made using those recommendations, has surprised me with it's repeatable, reproducible results in 3 firearms chambered for that.

Also found the same to be true in certain pistol cartridges, notably 10mm.

That brings me to the question, that hopefully someone here has insight into. Are those PMAL recommendations determined via empirical (real world experiment) results, or are they the result of an internal ballistics calculation?

This leading up to desiring a method, by which I could reference a given cartridge, bullet weight, and powder type, and have my own PMAL purely by predicted calculation.

Moreover, is this a function of QuickLoad? I've been considering purchasing that program as of late, and just wondered if it had provision for PMAL recommendations.

Thanks to all for reading my request here.

[wv109323]

The Lyman manual I have explains how they arrive at some of the conclusions.The PMAL is based on lab results of Standard Deviation, Average Velocity,Uniformity or Consistency of the Pressure Curve for each powder tested and actual accuracy results of loads tested in their lab.

[Rocky Raab]

That's correct. All other things being equal, a load that produces the most consistent pressure curve shape, peak pressure, and velocity is liable to be very accurate. It cannot overcome poor bedding, a bad crown, loose sights, or a jerk on the trigger though LOL!

[swheeler]

QUOTED FROM LYMAN CAST BULLET HANDBOOK, Third Edition

"Accuracy loads:
When a load is noted as such in the data tables proper, it means that the given combination of components produced the most uniform internal balistics of any load tested utilizing that particular bullet design. Unless noted in "Comments", the accuracy load was not fired at targets. The load, however, does have a high potential- assuming all external factors are optimum- for producing outstanding accuracy since uniform internal ballistics are critical to accuracy on target. You cannot have one without the other."

page 123

[Larry Gibson]

assuming all external factors are optimum

.....and that is the rub. You can have many an excellent load at HV based on internal ballistics.....however, it's in that phase called "external ballistics that thing occur that negatively impact accuracy. Note that Lyman does not any longer shoot test groups to measure actual accuracy.

Larry Gibson

[zardoz]

Thanks for the replies.

OK, from what I gather here, the PMAL is determined via internal ballistics computation.

After a bit more searching, I found another software package called RSI Lab which looks interesting. It combines the software package, with chronograph data, and also internal pressure data obtained via a strain gauge. Interesting. I had used strain gauges in a lab experiment back in my college days, to correlate metal characteristics with an equation using Poissons ratio. Surprised I remembered that after a quarter century.

I see where the load density ratio is used to a certain extent to predict PMAL. I guess what I'm thinking is an equation that utilizes burn rate, cartridge size and shape, bullet size and shape, barrel length, etc. Probably gets fairly complex. I realize that predicted results are just that. Even if I could get a +/- 5% accuracy plot versus real results, that would be peachy.

[Larry Gibson]

zardoz

You can predict, equate or guess all you want but the actual results will be, most often, different. The Lyman PMALs are also predicted from all of that information. One thing your pridiction will have a problem with is ignition consistency and where a particular powder will begin to burn efficiently. I also measure all the above via an Oehler m43. I also, at one time thought "priedictions" would come easy based on accumilation of data which should show "trends". Well that was a good theory.......there are too many variables to make predicitons. I can "guess" but I've found I'm batting only around 60 - 70% correct, much lower than your expected +/- 5%.

With easily ignitable powders I can tell you with a pretty certain assurance at what pressure level that powder will start burning efficiently and give good ignition. However, with the variables I can not accurately predict the load for a set of componants. Only actual testing gives the answer with the "guess" being quite a bit off sometimes. With powders that I have not extensively tested, particularly ball powders and the slow burners, I don't even bother guessing anymore....straight to testing for those it is.

There are some absolutes in this game which are predictable. I don't think this is going to be one that is predictable. However, not meaning to discourage you at all as you may surprise me.

Larry Gibson

[oldgeezershooter]

I can shoot the same load out of my Savage 110 25-06 and my Ruger#1 25-06 and there is a world of difference, It's best to experiment starting with their recommendations.
I found an excellent load for my 223 using the Lee data that came with the dies. 25gr. of Varget with a 55gr.boatail I never had to change anything and it's a tackdriver.